LVR Series of PolySwitch Devices

5/1/2003 Edited by PE Tech Staff LVR Series of PolySwitch™ Devices The LVR Series of PolySwitch® resettable devices from Raychem Circuit Protection, a unit of Tyco Electronics, is designed for use in line voltage applications. The polymeric positive temperature coefficient (PPTC) devices are rated at 240Vac, permitting maximum voltages of up to 265Vac, and are available in hold currents from 50mA to 400mA. In addition, they help protect against both overcurrent and overtemperature faults on the primary side of power supplies and transformers.

The LVR device was developed to help prevent damage to control boards and components by limiting current in the event of a load-side short-circuit or overdraw, or improper incoming voltage. Unlike a single-shot current fuse, the resettable LVR device can help protect against conditions where faults may cause a rise in temperature with only a slight increase in current draw. When installed on the primary side of the circuit, in proximity to potential heat-generating components such as magnetics, FETs, or power resistors, the LVR device can help provide both overcurrent and overtemperature protection with a single installed component.

The properties of the LVR device can provide distinct benefits in transformer protection designs. Its surface temperature in the high resistance state is well within the range of most transformer winding insulation ratings. This low temperature operation, combined with small size, low resistance and good thermal shock tolerance, allow it to be mounted in direct contact with the transformer windings for a faster response to potential fault conditions.